1. Field of the Invention
The present invention relates to a wafer loading/unloading device which attaches a wafer to be polished to a polishing head and which receives the wafer that has undergone polishing on the polishing head from the polishing head, and to a method of producing wafers by using this apparatus.
2. Description of the Related Art
Generally speaking, in a wafer polishing apparatus for polishing the surface of semiconductor wafers, a wafer polishing head holding the wafer and a platen to which a polishing pad is attached are opposed to each other, and polishing is effected by causing the wafer polishing head to make planetary motion on the polishing pad while pressing the surface of the wafer against the polishing pad and supplying slurry containing abrasive.
As shown in FIG. 12, an example of such a polishing head comprises a head main body 53 composed of a top plate portion 51 and a cylindrical peripheral wall portion 52 fastened to the outer periphery of the top plate portion 51, a diaphragm 54 consisting of an elastic material such as rubber stretched inside the head main body 53, a pressure adjusting mechanism 56 for adjusting the pressure in a fluid chamber 58, a disc-like carrier 55 fastened to the lower surface of the diaphragm 54, and an annular retainer ring 57 concentrically arranged in the outer periphery of the carrier 55.
The carrier 55 and the retainer ring 57 are respectively fixed to a carrier fixing ring 59 and a retainer ring fixing ring 62 provided on the upper side of the diaphragm 54, and the retainer ring 57 is arranged concentrically, with a slight gap being provided between the outer peripheral surface of the carrier 55 and the peripheral wall portion 52. When polishing a wafer, a wafer 70 is attached, for example, by vacuum suction, to a wafer attachment sheet 71 provided on the lower side of the carrier 55, with its outer periphery being engaged with the retainer ring 57. Then, the surface of the wafer 70 is brought into contact with a polishing pad 63 attached to the upper surface of a platen 61, and polishing is conducted by rotating a wafer polishing head 50 while supplying slurry containing abrasive.
In many cases, the wafer 70 is automatically attached to the lower surface of the polishing head 50 by means of a wafer loading device having a disc-like wafer support portion. At this time, the wafer 70 is accommodated in a wafer cassette, and extracted from the wafer cassette by a wafer extracting mechanism before it is conveyed to the wafer loading device. Then, the wafer 70 is conveyed to a position below the polishing head 50 by the wafer loading device, and the wafer support portion is brought close to the polishing head 50, whereby the wafer 70 is attached to the polishing head 50.
When the process for polishing the wafer 70 has been completed and the polishing head 50 is raised so as to be separated from the polishing pad 63, a wafer unloading device 81 having a disc-like wafer support portion 80 is arranged below the polishing head 50, as shown in FIG. 13, in order to receive the wafer 70 which has undergone the polishing process. Then, the wafer 70, which has been released from the attraction by the polishing head 50, is supported on the wafer support portion 80. The wafer support portion 80 supporting the wafer 70 moves so as to approach a robot arm 82 for conveying the wafer 70 to the next step. A suction mechanism is formed at the forward end 82a of the robot arm 82, and the wafer 70 is held by being sucked by the suction mechanism at the forward end 82a, and conveyed to the next step.
When the wafer 70 is attracted by the robot arm 82, the robot arm 82 first pressurizes the upper surface of the wafer 70, and stabilizes the surface with which the wafer 70 is attracted by the robot arm 82. Then, the upper surface of the wafer 70 is attracted by the suction mechanism at the forward end 82a of the robot arm 82, whereby the wafer 70 is held and conveyed to the next step.
When attaching the wafer 70 to the polishing head 50 by using this wafer loading device, the wafer loading device must perform the positioning correctly at the time of attaching the wafer 70 before the wafer 70 can be engaged with the retainer ring 57 in a stable manner. In this process, a high level of machining accuracy is required of each portion of the wafer loading device and high accuracy is required of each drive section.
When transferring the wafer to the robot after detaching the wafer 70 from the polishing head 50, the robot arm 82 is brought into press contact with the wafer 70 so as to attract the wafer 70 in a stable manner. At this time, a moment acts on the robot arm 82. However, since the robot arm 82 is in the form of a thin plate, it is subject to bending, so that it is brought into contact with the wafer 70 in an unstable manner. Further, since the robot arm 82 repeats bending, the service life of the robot arm 82 is rather short.
Further, foreign matter such as polishing swarf generated at the time of polishing the wafer adheres to the wafer 70 and the lower side of the polishing head 50. Due to this foreign matter, there is naturally the danger of the wafer 70 and the polishing head 50 being damaged. Furthermore, when the foreign matter is dried, it sticks to the lower side of the polishing head 50, etc., so that much effort is needed to perform cleaning.
The present invention has been made with a view to above problem in the conventional technique. Accordingly, it is an object of the present invention to provide a wafer loading/unloading device which is capable of performing positioning and mounting easily and in a stable manner when attaching the wafer to the polishing head and which can receive the polished wafer in a stable manner and pass it to the next step and a method of producing wafers.
To achieve the above object, there is provided in accordance with the present Invention a wafer loading/unloading device for attaching a wafer to a polishing head and receiving the wafer from the polishing head, comprising a main body portion formed in a circular configuration in plan view and adapted to support a wafer, a swinging arm supporting the main body portion, a swinging shaft for supporting the swinging arm so as to be horizontally swingable, an arm ascending/descending mechanism for supporting the swinging arm so that it can ascend and descend with the main body portion, and a swinging drive source for driving the swinging shaft, wherein the main body portion is equipped with a disc-like wafer support portion and an action force absorbing mechanism for absorbing a vertical force acting on the wafer support portion.
In accordance with the present invention, the wafer support portion is equipped with an action force absorbing mechanism which is a mechanism for absorbing a vertical force acting on the wafer support portion, so that the impact when the wafer is attached to the polishing head is mitigated. Thus, the wafer and the polishing head are prevented from being damaged. Further, when transferring the wafer to the robot after detaching the wafer from the polishing head, if the robot arm presses the wafer downward, the wafer also moves downward due to the action force absorbing mechanism. As a result, the moment acting on the robot arm in the form of a thin plate is reduced, and the forward end portion of the robot arm can be brought into contact with the upper surface of the wafer, with the robot arm not being bent. Thus, the robot arm can reliably hold the wafer, so that the wafer can be passed to the next step in a stable manner.
Further, the wafer support port-on is of a floating construct which is equipped with a swinging mechanism for swingably supporting the wafer support portion. Thus, when attaching he wafer, if the carrier lower surface which is the wafer attachment surface of the polishing head is positionally somewhat deviated from the wafer, the wafer support portion which is of a floating construction swings, whereby the wafer can be attached to the lower surface of the carrier in a stable manner. Further, due to the floating effect of the wafer support portion, the wafer and the carrier lower surface are not abruptly brought into contact with each other. Thus, the wafer and the carrier lower surface are prevent from being damaged.
The loading/unloading device of the present invention is equipped with an engagement portion which restricts excessive movement in the horizontal and vertical directions of the wafer support portion, so that if great disturbance acts on the wafer support portion, and the wafer support portion swings greatly, an excessive movement of the wafer support portion is prevented by the engagement portion. Thus, no interference is generated between the wafer supported by the wafer support portion and each portion of the polishing head and the device. Thus, damage to the wafer is prevented.
The loading/unloading device of the present invention is equipped with an annular retainer ring engagement portion which is provided above the wafer support portion and which is capable of being engaged with the retainer ring of the polishing head, so that when attaching the wafer to the polishing head, the retainer ring engagement portion and the retainer ring lower surface are engaged with each other. At this time, the wafer support portion is of a floating structure using the retainer ring engagement portion as a reference. Thus, even if at the time of attaching the wafer the carrier lower surface which constitutes the wafer attachment surface of the polishing head is positionally somewhat deviated from the wafer, the positioning of the wafer supported by the swinging wafer support portion is accurately effected, with the wafer being guided by the retainer engagement ring and the inner peripheral wall of the retainer ring. Thus, the wafer is attached to the carrier lower surface in a stable manner.
The distance between the wafer support portion and the retainer ring engagement portion is set to be larger than the wafer upper surface and the polishing head attachment surface a the time of attaching or detaching the wafer to or from the polishing head, so that before the wafer is attached to the carrier which forms the wafer attachment surface of the polishing head, the retainer ring engagement portion is not brought into contact with the wafer support portion. Thus, the wafer support portion continues to be swung until the wafer is attached to the carrier. That is, the positioning of the wafer is effected in a stable manner due to the floating effect.
In the loading/unloading device of the present invention, a cleaning mechanism for cleaning at least one of the polishing head and the wafer is provided in the vicinity of the center of the main body portion, so that it is possible to remove foreign matter from the lower portion of the polishing head and the carrier lower surface before the wafer is attached to the polishing head or it is detached to the polishing head. Thus, it is possible to prevent defective adhesion between the wafer and the carrier due to foreign matter. Further, it is possible to prevent damage to the wafer due to foreign matter. The foreign matter adhering to the lower surface of the wafer which has undergone polishing is removed by cleaning by the cleaning mechanism. Thus, the wafer is supported by the wafer support portion in a stable manner.
Further, the main body portion equipped with the cleaning mechanism also swings to the lower side of the polishing head to which no wafer is attached. By cleaning the polishing head to which no wafer is attached by the cleaning mechanism, it is always possible to prevent adhesion of foreign matter.
In the loading/unloading device of the present invention, there is provided at the upper end of the wafer support portion a second cleaning mechanism for cleaning the upper surface of the wafer detached from the polishing head, so that both the upper and lower side of the polished wafer are cleaned. That is, since the wafer upper surface which is the surface to which the robot arm for conveyance to the next step is also cleaned, it is possible to prevent a deterioration in the attraction force of the robot arm due to foreign matter. Further, it is possible to prevent damage to the wafer due to foreign matter.
The wafer support portion is equipped with a wafer engagement portion for restricting the horizontal movement of the supported wafer, so that the wafer is supported by the wafer support portion in a stable manner.
In accordance with the present invention, there is provided a method for producing wafers of the type which includes a step for attaching the wafer to a polishing head to perform polishing, the method comprising the steps of arranging below the polishing head a main body portion equipped with a disc-like wafer support portion, an action force absorbing mechanism for absorbing a vertical force acting on the wafer support portion, and an annular retainer ring engagement portion provided above the wafer support portion and capable of being engaged with the retainer ring of the polishing head, cleaning the polishing head by spraying cleaning liquid from a cleaning mechanism provided in the vicinity of the center of the main body portion, moving the main body portion from below the polishing head to support an unpolished wafer on the wafer support portion, arranging it again at the position below the polishing head, bringing the main body portion close to the polishing head to bring the retainer ring engagement portion into contact with the retainer ring of the polishing head, bringing the wafer support portion close to the Polishing head while swinging it to thereby attach the wafer to the polishing head, and polishing the wafer by rotating the polishing head while pressing the wafer against a polishing pad.
In accordance with the present invention, the unpolished wafer supported by the wafer support portion which is of a floating structure is guided by the inner peripheral wall of the retainer ring engagement portion and the inner peripheral wall of the retainer ring and attached to the polishing head reliably and accurately. Further, since the wafer is attached to the polishing head after cleaning it by the cleaning mechanism, the wafer is prevented from being damaged and the attachment is effected in a stable manner.
Further, in accordance with the present invention, there is provided a method for producing wafers of the type which includes a step for detaching a wafer polished by a polishing head, the method comprising the steps of arranging below the polishing head with the polished wafer a main body portion equipped with a disc-like wafer support portion, and an action force absorbing mechanism for absorbing a vertical force acting on the wafer support portion, cleaning the wafer lower surface and the polishing head by spraying cleaning liquid from a cleaning mechanism provided in the vicinity of the center of the main body portion, detaching the wafer from the polishing head to support is on the wafer support portion, cleaning the wafer upper surface by spraying cleaning liquid from a second cleaning mechanism provided at the upper end of the wafer support portion, passing the wafer whose upper and lower surfaces have been cleaned to a robot arm of the next step while absorbing the vertical force by the action force absorbing mechanism, and arranging the main body portion below the polishing head again to clean the polishing head by the cleaning mechanism.
In accordance with the present invention, the wafer which has undergone the polishing process is passed to the next step after its upper and lower surfaces have been cleaned, so that damage to the wafer is prevented. Further, the polishing head to which no wafer is attached yet is cleaned with cleaning liquid sprayed from the cleaning mechanism and is prevented from being dried. Thus, foreign matter is prevented from sticking to the polishing head, and damage to the wafer at the time of attaching it to the polishing head is prevented.